Typical acrylic pressure sensitive adhesive formulations are copolymers of alkyl ester monomers, a functional monomer such as acrylic acid, and may be crosslinked using, for example, aluminum or titanium chelates. These adhesives may be further tackified to improve adhesion on different types of substrates, although usually with limitations in resistance to degradation and aging for most graphics and industrial tape applications in which acrylic solutions are conventionally used.
U.S. Pat. Appl. No. 2005/0142357 discloses a high strength pressure sensitive adhesive comprising a blend of a cross-linked liquid polymer, at least one tackifying resin which is compatible with the liquid polymer, and at least one resin which is incompatible or at least partially incompatible with the liquid polymer. Although the formulated products described in this disclosure provide very high performance at ambient temperature, their high temperature performance will be limited by the Tg of the incompatible phase.
U.S. Pat. No. 5,625,005, No. 6,642,298 and No. 6,670,417 disclose hybrid rubber-acrylic pressure sensitive adhesives described as having good UV resistance and aging characteristics along with high adhesion to non-polar surfaces.
Despite these advancements in the art, there continues to be a need for high performance pressure sensitive adhesives having high adhesion and heat resistance properties that are able to meet higher requirements in applications such as industrial tapes and transfer films. There is also a need for a pressure sensitive product with extremely good performances in other areas, such as impact resistance.
Pressure sensitive adhesives that will pass the UL-972 Testing for Burglary Resistant Glazing Materials standard would provide for the manufacture of glass/plastic laminates exhibiting a minimum amount of delamination of a glass substrate from a polyester facestock following impact. This requirement translates into a strong bonding of the pressure sensitive adhesive under a very high speed delamination process, i.e., about 10000× fold higher than regular peeling test speed of 12″/min. Current pressure sensitive adhesive products used for this application do not give satisfactory results when tested by the UL-972 standard.
There is thus a need in the art for pressure sensitive adhesives that will pass the UL-972 standard when used to bond glass to plastic. The present invention addresses this need.